The instant invention relates to a thermostatic switch construction and more particularly to a construction for a single pole double throw thermostatic switch of the type actuated by a bimetallic disc which flexes in response to a predetermined temperature change, and a method of assembling and adjusting the same.
Single pole double throw thermostatic switches have found wide use in many applications, particularly in appliances and the like where electrical continuity must be alternatively effected between a first terminal and second or third terminals in response to a predetermined temperature. Traditional constructions for switches of this general type have included a main switch body and a bimetallic disc mounted at one end thereof and which exerts a flexing action in response to a predetermined temperature change. A pair of spaced fixed contacts and a resilient contact arm are mounted in the main body with the resilient arm being normally biased to engagement with the first of said fixed contacts, but being movable to a point of engagement with the second of said contacts. Communication between the resilient arm and the bimetallic disc is provided by a transfer pin which travels in a bore within the main body and operates to move the resilient arm from a position of engagement with said first fixed contact to a position of engagement with the second fixed contact. In this manner electrical continuity is alternatively effected between a first external terminal electrically connected to the resilient contact arm and second or third external terminals electrically connected to said first and second fixed contacts respectively.
Obviously, the effectiveness of thermostatic switches of this general type depends on the reliability of the switch to alternatively provide complete electrical continuity between the respective pairs of external terminals in response to a predetermined temperature change. One of the constraining factors in this regard is the precise setting of the gap between the pairs of fixed contacts. Since the movement of the resilient contact arm is controlled by corresponding movement of the disc, the amount of travel of the resilient arm is generally constant. Therefore, in order to insure the proper switching action with the resilient arm, the fixed contacts must be precisely positioned so that complete electrical continuity is effected and interrupted alternatively between the fixed contacts.
Previously known thermostatic switch assemblies have included an external adjustment screw which is engageable with one of the fixed contacts in the switch to effect the proper setting of the gap after the switch has been completely assembled. However, since the gap in this type of switch must be set after the switch has been completely assembled, it is impossible to observe the interaction between the adjustment screw and the fixed contacts and hence the reliability of the finished switch may in some cases be lessened as a result of improper adjustment of the screw. Furthermore, since the adjustment of the gap between the contacts is effected with an adjustment screw (usually of self-tapping type screw) dirt and contaminants can enter the cavity in the switch assembly around the threads of the screw and in some cases may damage or contaminate the contacts and thereby detract from the degree of electrical continuity effected by the switch.
The instant invention relates to a novel switch construction and method of assembling the same wherein the gap between the fixed contacts within the cavity is set before the switch is completely assembled thereby provide a more reliable setting of the gap. Since the gap is set prior to the final assembly of the switch, the entire gap setting operation may be completely observed to assure proper setting. Furthermore, since the gap is set at an intermediate point in the assembly of the switch, the necessity for providing an external screw on the switch is eliminated allowing the entire switch assembly to be better sealed to prevent dirt and contaminants from entering the interior thereof.
Accordingly, it is an object of the instant invention to provide a bimetallic disc type single pole double throw thermostatic switch construction wherein the gap between the fixed contacts in the switch assembly is preset by bending one of said contacts prior to the final assembly of the switch.
Another object of the instant invention is to eliminate the necessity for incorporating an external adjustment screw in a single pole double throw thermostatic switch construction.
A still further object of the instant invention is to provide an effective method for setting the gap between the fixed contacts in a bimetallic disc type single pole double throw thermostatic switch.
A still further object of the instant invention is to provide a method of assembling a single pole double throw thermostatic switch wherein the gap between the fixed contacts is set prior to the completion of the assembly of the switch.